The formation of epitaxial semiconductor structures wherein preferential growth planes are employed have been known in the field for some time. Two illustrative examples are U.S. Pat. Nos. 3,884,733 and 3,855,690 wherein arrays of devices having particular shapes useful for optical purposes are formed by growing epitaxial material on a substrate using a crystallographic plane that exhibits preferential growth and which provides an optically desirable face. Heretofore in the art, however, the region produced by the preferential growth plane has been exposed.